1. Field of the Invention
The present invention relates to a device for storing rectangular sheets to be fed into a sheet conveying path in an image forming apparatus such as copying apparatus or the like, which can change the orientation of the sheets in accordance with longitudinal and lateral feeds of the sheets.
2. Description of the Related Art
Generally, copying apparatuses are provided with a device for storing rectangular sheets such as papers or transparent films which are to be fed into a sheet conveying path in a main body of the copying apparatus. An exemplary sheet storing device is equipped with a plurality of sheet cassettes for different sized of sheets, such as sheets of A3, B4, A4, and B5 sized etc. In order to shorten a time necessary for conveying the rectangular sheet through the conveying path of the copying apparatus, it is desirable to perform lateral feed of the sheet in that the short sides of the rectangular sheet are parallel to the feeding direction of the sheet rather than longitudinal feed of the sheet in that the long sides of the rectangular sheet are parallel to the feeding direction. For this purpose, several types of copying apparatus have been constructed to perform lateral feed of sheets even when the sheets are of relatively large size such as B4 or A3 size.
However, such a construction for performing lateral feed of relatively large sheets causes other functional units, such as a photo sensitive drum, conveying rollers, a developing unit, a fixing unit etc., of the copying apparatus to be made in large size correspondingly, resulting in an increase of the copying apparatus in size as well as an increase of manufacturing cost thereof. Accordingly, in general, copying apparatuses in which relatively large sheets, e.g., sheets of B4 or A3 size can only be fed longitudinally have been widely used.
In this case, however, particularly in copying apparatuses having functions of reduction and enlargement of size such as zooming up/down function etc., it is necessary for size-reduction copying to use cassettes of B5R-, and A4R-size types for the longitudinal feed of sheets of B5 and A4 sizes, while it is also necessary, when feeding speed is taken into consideration, to use cassettes of B5-, and A4-size types for the lateral feed of sheets of B5 and A4 sizes.
In order to satisfy the above-mentioned requirements, a sheet feeder must be constructed to receive all of the above-mentioned various cassettes, or replacement of cassettes for each purpose will be required. This means that the sheet feeder must be fabricated in much larger size at high cost or troublesome operations for replacing the cassettes are required.
As disclosed for example in Japanese Unexamined Patent Publications (KOKAI) No. 56-59245, laid open in 1981 and No. 56-59251, laid open in 1981, there has been proposed a sheet feeder for eliminating the abovementioned problems, in which a rotatable tray or cassette for stacking or storing thereon sheets of B5-, or A4-size is used for both longitudinal and lateral feeds of the sheets. The common cassette disclosed is supported by a support member for rotation about an axis which is located at a fixed position with respect to the support member.
In this case, however, when the rotatable cassette is rotated between a first or longitudinal feed-out position and a second or lateral feed-out position with respect to the conveying path of the sheet in the copying apparatus, the distance between a pickup roller and the cassette varies with the positions of the cassette. Accordingly, after arriving of the rotatable cassette at its lateral feed-out position, the rotatable cassette as well as the support member must be moved toward the pickup roller, or the pickup roller must be moved toward the cassette to reduce the distance therebetween. In this case, however, it is necessary to provide drive means for moving the rotatable cassette or the pickup roller in addition to drive means for rotating the cassette, so that the construction of the sheet feeder becomes complicated and, thus, the manufacturing cost thereof is increased. Moreover, since a certain time for the additional movement of the cassette or the pickup roller for decreasing the distance therebetween is required, it becomes difficult to start promptly the feeding of sheet after rotational displacement of the cassette. Especially, in the case that the pickup roller is moved toward the cassettes which is located at its lateral feed position, the conveying path of the sheet in the copying apparatus becomes longer due to the retraction of the leading edge of the sheet in the cassette from the position thereof when the cassette is located at its longitudinal feed position, resulting in an increase of time for conveying the sheet.
As an example of construction for solving the abovementioned defects, it may be considered to provide a tray drive unit in which a movable tray or cassette for stacking or storing thereon sheets is rotatably supported on the movable support member which, in turn, is movably supported on a base member in a direction generally parallel to the feeding direction of the sheet, and in which a reciprocating member is reciprocatingly driven by a drive unit along a guide shaft in a direction generally perpendicular to the feeding direction of the sheet while being in engagement with the movable tray or cassette at a position near the intersection of a longitudinal feedout side and a lateral feed-out side of the movable tray or cassette. In this construction, the reciprocating motion of the reciprocating member causes the movable tray or cassette to be rotated while being moved in a direction generally parallel to the feeding direction of the sheet. Accordingly, the longitudinal and lateral feed-out sides of the movable tray or cassette will be directly moved to a constant position with respect to the pickup roller.
In this case, however, it is considered that further problems will occur. Namely, in a case that a large number of sheets are loaded on the movable tray or cassette, an increased inertia force of rotation of the movable tray will be generated due to their weight. Thus, the reciprocating member may run over the predetermined position due to slippage of the reciprocating member against the shaft, causing the movable tray or cassette to be postured in inclination with the direction of the feeding direction of the sheets.